The present invention relates to rotary fluid pressure devices, and more particularly, to such devices in which there is a main torque transmitting drive shaft coupled to the output shaft of the device.
Although the invention may be utilized in connection with various fluid pressure devices, it is especially adapted for use with low speed, high torque gerotor motors, and will be described in connection therewith.
Furthermore, although the present invention can be utilized with rotary fluid pressure devices having various types of valving, it is especially advantageous when used with devices having hollow, generally cylindrical spool valves wherein the valving action occurs at the interface of the valve spool and the adjacent housing surface.
Low speed, high torque gerotor motors have been in commercial use for many years and are especially suited for applications such as vehicle wheel drives, winch drives, and providing rotary torque to various other vehicle implements. Such motors have been commercially successful partially because the gerotor gear set is uniquely suited to provide the desired low speed, high torque output in a compact device which is relatively inexpensive.
However, in many of the applications for gerotor motors of the type noted above, it has been found desirable to be able occasionally to operate the motor in some mode other than its normal, operating mode. For example, if the motor is being used to provide torque to the drive wheels of a vehicle, when the vehicle is to be towed, it would be quite useful to be able to operate the motor in a free-wheeling mode. An attempt by the prior art to provide a motor capable of operating in a "free-wheeling" mode is illustrated by U.S. Pat. No. 4,435,130. Although the device disclosed therein is described as having a free-wheeling mode, the actual mode of operation is to establish a short-circuit flow path from the inlet port to the outlet port, across the commutating valve. Because the motor output shaft is still connected to the rotating element of the gerotor, the motor is not actually in a free-wheeling mode.
As another example of a desired mode, if the motor is being used to drive a winch, it is quite useful to be able to operate the motor in a locked mode of operation, to provide a positive load-holding capability. In order to achieve a locked mode of operation, it has been the normal practice to utilize some sort of mechanical brake in association with the output shaft of the gerotor motor. However, such an arrangement adds substantially to the overall size and expense of the motor package.
It is also desirable when two or more such motors are being used in a single circuit to be able to block flow through one of the motors, if the motors are in parallel, or to be able to short-circuit one of the motors, if the motors are in series. In the prior art, when such parallel and/or series operation has been desired, it has typically been achieved by means of the externally-plumbed flow control valve arrangement for controlling the flow of fluid to each of the motors. Achieving blocked flow of short-circuit flow in this manner can add substantially to the complication and expense of the flow control valve arrangement.